The present invention is directed in a broad aspect to column or tower packings for use in packed column chemical processing operations such as absorption, desorption, distillation, extraction, scrubbing, drying, cooling, water treatment and the like. More particularly, the present invention is directed to a new and improved high efficiency, high performance packing body for use in such chemical apparatus.
Column or tower packing bodies have been long used to enhance the efficiency and productivity of a variety of chemical processes involving fluid interaction. Generally speaking, packing bodies are a contact media which is necessary for certain types of chemical processing operations such as the aforementioned distillation and scrubbing procedures. In such processing operations, a stream of liquid is brought together with a stream of gas or another liquid in a confined environment such as a column, tower, or other vessel so as to accomplish an exchange of materials or heat or both between the two streams of fluid. On a microscopic scale this transfer of mass or heat is driven by the laws of physical chemistry. On a larger or industrial scale this transfer is significantly influenced by the gross physical properties of the liquid or gas streams and their mixing environment--large areas of fluid contact and interaction increasing the transfer rate and efficiency of a given process and restrictive fluid flow decreasing its overall performance.
In order to increase the efficiency and practicality of these chemical processing operations, a variety of column packing materials have been used in the past to enhance the essential contact between the two streams of material involved. These prior art packing materials range from the early used gravel and broken glass to man made bodies having unique geometric shapes such as perforated cylinders, saddles, helical rings and spiked or latticework balls. Depending on the desired application, these latter synthetic packing bodies are made of either plastic, metal or ceramic, and range in size from a few centimeters to tens of centimeters across.
The performance of packed columns or towers is significantly affected by the column packing material used. Because packed columns are often the most critical step in a chemical processing procedure, the performance of the packed column can significantly affect both product yield and production rate as well as the overall economic viability of the process. The most important parameters for judging the performance of a column packing are its mass or heat transfer rate and its pressure drop. The latter parameter dictating the energy requirements necessary to maintain the packed column operation. The best performing column packing provides the maximum mass or heat transfer rate with a minimum or acceptable pressure loss.
A number of factors affect the performance of column packing materials per se. These factors are interrelated and are products of the physical geometry of the individual packing bodies making up the total packing material loaded into a column or tower. These factors are: interlocking, channeling, chimneying, fouling, nonuniform flow, wetting, and flooding.
Briefly stated, interlocking occurs when the individual bodies of the column packing materials mesh together within the packed column. This occurs when the packing bodies lack geometric uniformity and contain projections or open areas. Interlocking creates uneven fluid flow patterns, dead spaces where solid deposits may build up, and reduces available surface area thereby reducing column efficiency.
Channeling refers to an excessive amount of liquid flowing along the outer surfaces of a packing material. It occurs when the packing bodies are nonuniformly situtated within a column or tower. Similarly, chimneying refers to an excessive amount of gas passing through open areas in unevenly situated packing materials. In both cases, the fluid flow patterns are distorted and result in reduced transfer rates and high pressure drops and a reduction in column efficiency.
Fouling occurs when deposits of particulate matter accumulate on the surfaces of the packing material or in the dead spaces between packing materials. Reduced fluid flow accentuates this problem. By reducing available surface area and plugging a portion of a packed column fouling will also reduce transfer rates and increase pressure drop within a column. All of these factors result in an overall nonuniform liquid or gas flow which reduces column performance.
Wetting the column packing surface to provide gas/liquid or liquid/liquid contact is essential to the operation of a packing material. Packings which interlock will leave large fractions of their surface area unexposed to wetting. For a given packing material there is a minimum liquid flow required to produce approximate total wetting of the available surface area. This minimum liquid flow is called the "wetting point".
Conversely, packing materials inherently restrict a certain amount of liquid flow. This restriction varies with the liquid and gas flow rates. It reaches its maximum or "flooding point" when the gas velocity exceeds a certain limit for a given liquid flow rate. This gas velocity is called the "flooding velocity" and is utilized in the design of column size and gas velocity for a given chemical process.
An ideal column packing would offer the lowest wetting point and the highest flooding point under given column operating parameters. This ideal packing would operate with a minimum of liquid flow and a maximum gas velocity which enables a chemical process to be carried out using a smaller packed column. As a result, initial capital outlay and subsequent operating expenses would be reduced.
It has been commonly accepted in the art for over 60 years that a high transfer rate can only be achieved with a column packing which provides a large surface and a correspondingly large pressure drop due to restricting gas flow within the column. Thus, the ideal prior art column packing materials are a tradeoff between efficiency and overall performance. Accordingly, it is a principal object of the present invention to provide a column packing body which provides a high transfer rate with a low pressure drop.
It is a further object of the present invention to provide a column packing body which resists interlocking and deformation and the attendant problems of channeling, chimneying, fouling and nonuniform fluid flow.
It is a further object of the present invention to provide a column packing body with a surface area that will achieve approximate total wetting of the packing surface at a low wetting point and which will also provide a high flooding point under column operating conditions.